geodesic_cpp_03_02_2008/geodesic_constants_and_simple_functions.h

//Copyright (C) 2008 Danil Kirsanov, MIT License
#ifndef GEODESIC_CONSTANTS_20071231
#define GEODESIC_CONSTANTS_20071231

// some constants and simple math functions

#include <assert.h>
#include <math.h>
#include <limits>
#include <fstream>

namespace geodesic{

#ifndef M_PI
#define M_PI 3.14159265358979323846
#endif

//double const GEODESIC_INF = std::numeric_limits<double>::max();
double const GEODESIC_INF = 1e100;

//in order to avoid numerical problems with "infinitely small" intervals,
//we drop all the intervals smaller than SMALLEST_INTERVAL_RATIO*edge_length
double const SMALLEST_INTERVAL_RATIO = 1e-6;        
//double const SMALL_EPSILON = 1e-10;


inline double cos_from_edges(double const a,            //compute the cosine of the angle given the lengths of the edges
                             double const b,
                             double const c)
{
    assert(a>1e-50);
    assert(b>1e-50);
    assert(c>1e-50);

    double result = (b*b + c*c - a*a)/(2.0*b*c);
    result = std::max(result, -1.0);
    return std::min(result, 1.0);
}

inline double angle_from_edges(double const a,          //compute the cosine of the angle given the lengths of the edges
                               double const b,
                               double const c)
{
    return acos(cos_from_edges(a,b,c));
}

template<class Points, class Faces>
inline bool read_mesh_from_file(char* filename,
                                Points& points,
                                Faces& faces)
{
    std::ifstream file(filename);
    assert(file.is_open());
    if(!file.is_open()) return false;
    
    unsigned num_points;
    file >> num_points;
    assert(num_points>=3);

    unsigned num_faces;
    file >> num_faces;

    points.resize(num_points*3);
    for(typename Points::iterator i=points.begin(); i!=points.end(); ++i)
    {
        file >> *i;
    }

    faces.resize(num_faces*3);
    for(typename Faces::iterator i=faces.begin(); i!=faces.end(); ++i)
    {
        file >> *i;
    }
    file.close();

    return true;
}

} //geodesic

#endif  //GEODESIC_CONSTANTS_20071231